The present invention relates to a plasma display panel, in particular to a surface discharge type plasma display panel.
Recently, there has been a demand that a surface discharge type plasma display panel be put into actual use, i.e., for use as a color display device which is large in size but small in thickness. FIG. 6 is a plane view schematically illustrating the structure of a conventional surface discharge type plasma display panel. FIG. 7 is a cross sectional view schematically indicating the internal structure of the plasma display panel of FIG. 6.
Referring to FIG. 6, the conventional plasma display panel has a plurality of row electrode pairs 2, 2, each arranged along a display line L of a matrix array on the panel, in a manner such that each electrode pair 2, 2 has a discharge gap 11 formed therebetween. Further, along each display line L, there are formed several unit luminescent areas, each of which forms a picture element cells (discharge sell).
FIG. 7 is a cross sectional view taken along a line V--V in FIG. 6, illustrating some important portions of the conventional display panel of FIG. 6. As shown in FIG. 7, formed on the inner side of a front glass substrate 1 (serving as a front display plate), are a plurality of color filter layers 41R, 41G, 41B each consisting of an inorganic pigment material, a transparent overcoat 42 covering the color filter layers 41, a plurality of row electrode pairs 2, 2, a dielectric layer 3 covering the row electrode pairs 2, 2, a protection layer 4 consisting of MgO for covering the dielectric layer 3.
Each row electrode 2 includes a transparent electrode 2a consisting of a belt-like transparent conductive film of ITO having a relatively large width, and a metal electrode (bus electrode) 2b consisting of a metal film having a relatively small width. The metal electrode 2b is used to supplement the conductivity of the transparent electrode 2.
On the other hand, a rear glass substrate 5 is positioned spaced apart from the front glass substrate 1 so that a discharge space 8 is formed between the two substrates. As shown in FIG. 7, a plurality of column electrodes 6 are provided on the inner surface of the rear glass substrate 5 in a manner such that they are all orthogonal to the row electrode pairs 2, 2. In fact, each intersection of the row electrode pairs 2, 2 with a column electrode 6 forms a picture element cell. Further, a plurality of belt-like partitions 9 are provided between the column electrodes 6, so that the discharge space 8 is divided into several sections. In addition, a plurality of fluorescent layers (7R, 7G, 7B) are disposed in the discharge space 8 to cover the column electrode 6 and the partitions 9. Finally, after a noble gas is sealed into the discharge space 8, a plasma display panel is thus formed.
In use of the surface discharge type plasma display panel constructed in the above prior art, at first, an addressing process is performed by selected discharges between the column electrodes 6 and the row electrodes 2, so as to select lighting cells (in which wall charges are formed) and not-lighting cells (in which wall charges are not formed). After the addressing process, by alternatively applying discharge maintaining pulses to the row electrode pairs 2, 2 on all the display lines L, a surface discharge will occur every time the discharge maintaining pulses are applied to the lighting cells. Then, with the effect of the surface discharge, an ultraviolet light will occur, so that the fluorescent layer 7 is excited, thereby producing a visible light.
Conventionally, in order to improve a contrast and a color fineness of a surface discharge type plasma display panel, color filter layers 41R, 41G, 41B are usually provided on the inner surface of the front glass substrate 1, as shown in FIG. 7. However, if several color filter layers 41R, 41G, 41B are disposed on the inner surface of a front glass substrate 1, these color filters 41 are difficult to be made uniform in their thickness, because different color filter layers are usually manufactured with different requirements and have different optical characteristics. As a result, some irregularities will occur on the inner surface of the front glass substrate 1. To eliminate such irregularities, an overcoat layer 42 is often formed to cover up these color filters 41, but still fails to obtain a smooth and flat surface, unavoidably producing some shouldered portions of several microns. Consequently, as shown in FIG. 7, some undesired gaps 50 will be formed, resulting in a problem that a discharge in one cell will undesirably spread to an adjacent cell through such gap 50, hence causing a wrong discharge.